This application claims the benefit of Japanese Patent Applications No.2000-204226 filed Jul. 5, 2000 and No.2001-130229 filed Apr. 26, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to operation data creating methods and apparatuses for mobile communication systems and storage media, and more particularly to an operation data creating method and an operation data creating apparatus which create operation data for use in a handover process of a mobile station in a cellular mobile communication system, and to a computer-readable storage medium which stores a program for causing a computer to create the operation data.
2. Description of the Related Art
In a conventional cellular mobile communication system such as the personal digital cellular (PDC) system, communication services are provided by dividing a service area into relatively small radio zones called cells, as shown in FIG. 1. In other words, a wireless channel is set between a base station 200 which covers each radio zone and a mobile station 100 which is located within the zone, and a communication is made via the wireless channel which is set between the base station 200 and the mobile station 100.
A communication quality level between the mobile station 100 and the base station 200 is affected by a radio wave attenuation which is dependent upon a distance between the mobile station 100 and the base station 200 and a radio wave propagation loss which is dependent upon arrangements of surrounding geometrical features, buildings and the like. On the other hand, when communicating between the mobile station 100 and the base station 200, a receiving end requires a reception power which is greater than a predetermined value in order to receive and demodulate signals with a predetermined quality. Accordingly, an optimum base station 200 which is to communicate with the mobile station 100 changes with time as the mobile station 100 moves. For this reason, the mobile station 100 constantly searches for the base station 200 which can secure an optimum communication quality level, and when a base station 200 which can secure a better communication quality level is found, a so-called handover process is carried out to set a new connection between the mobile station 100 and the newly found base station 200.
In order to carry out the handover process, the mobile station 100 constantly searches for a base station 200 which is located in a neighborhood of the base station 200 with which the mobile station 100 is communicating and is capable of securing a better communication quality level. In order to notify information for identifying the base station 200 and information related to the mobile communication system to the mobile communication system 100, each base station 200 broadcasts the information using a control channel which is used in common by a large number of users (mobile stations 100). Hence, the mobile station 100 can search and identify the base station 200 by receiving the information from the control channel.
Known wireless access systems employed in the mobile communication system include frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). For the common control channel described above, different radio frequencies are allocated for each of the base stations 200 in the case of the FDMA and the TDMA, and different spread codes are allocated for each of the base stations 200 in the case of the CDMA. In other words, the mobile station 100 can search for the neighboring base stations 200 by successively receiving signals of predetermined radio frequencies or predetermined spread codes.
In order to maintain a high communication quality level between the mobile station 100 which moves and each of the base stations 200, the mobile station 100 must frequently search for the neighboring base stations 200. However, it is impractical to search for all of the radio frequencies or spread codes used within the mobile communication system, because this would require considerable time and power. Hence normally, each base station 200 notifies to the mobile station, as the operation data for the handover control, a table (hereinafter referred to as a neighboring zone table) which indicates the radio frequencies and the spread codes which are used as the common control channel by the other base stations 200 located in the neighborhood of the base station 200. The mobile station 100 searches the neighboring base stations 200 by referring to this neighboring zone table.
Conventionally, the neighboring zone table is created in the following manner.
The radio wave propagation state within the service area is evaluated by simulating the radio wave propagation based on the elevation data, geometrical feature data, information related to the base and mobile stations and the like which are stored for each local position (small region) within the service area. For example, techniques for evaluating the radio wave propagation state are proposed in Fujii, Asakura and Yamazaki, “Cell Design System for Mobile Communication”, NTT Docomo Technical Journal Vol.2, No.4, pp.28-34, 1995-01, and Oomatsuzawa and Yamashita, “Station Design Total Support System”, NTT Docomo Technical Journal Vo.4, No.1, pp.28-31, 1996-04.
Based on the evaluation result of the radio wave propagation state within the service area, an area where the radio wave reception level from each base station becomes greater than or equal to a predetermined level is determined as a territory of each base station. A base station of a territory which is adjacent to the territory of each base station which is determined in this manner, is determined as a neighboring base station of each base station. The neighboring zone table which is created indicates the neighboring base station which is determined for each base station.
The neighboring zone table (operation data for the handover control) which is created by the above described technique indicates a base station of a territory which is adjacent to a territory of a certain base station, as a related base station located in the neighborhood of the certain base station.
However, with respect to each base station, the neighboring zone table only indicates the base station of the territory which is adjacent to the territory of each base station. For this reason, it is difficult to reflect in detail the radio wave propagation state within the service area, which varies depending on the structure and arrangement of the buildings, the geometrical feature data and the like, in the neighboring zone data. Consequently, when carrying out the handover control using the neighboring zone table which is created in this manner as the operation data, it is not always the case that a high communication quality level is maintained.